The rider claims the car aborted a lane change, while the automaker claims the rider crashed by himself.

Oscar Nilsson of San Francisco has filed a lawsuit against General Motors concerning a crash between him and an autonomous Chevy Bolt that occurred Dec. 7, reports the Mercury News. The Bolt was occupied but driving in autonomous mode at the time of the crash.

Nilsson claims that the Bolt, being tested by General Motors subsidiary Cruise, signaled and began to change lanes to the left. Nilsson accelerated to pass on the right before the lane change was complete, which is legal under California's laws that permit lane splitting. The Bolt then aborted its lane change and moved right, back into the lane, colliding with Nilsson, he claims. The driver's hands were reportedly off the steering wheel the entire time.

The crash report that GM filed with the California DMV tells a different story than Nilsson's. General Motors acknowledges that the car had aborted a lane change and was operating in autonomous mode, but denies that this caused the crash. Rather, the report claims that Nilsson "moved into the center lane, glanced the side of the Cruise … wobbled, and fell over." The automaker also claims that Nilsson was found to be at fault in the crash for making an unsafe pass.

What actually caused the crash is hard to say and will be up to the courts to decide. It's entirely possible that Nilsson's story is true, and the autonomous Bolt did not properly detect a lane splitting motorcycle occupying part of its lane and failed to give it enough room. On the other hand, it's just as likely that Nilsson got distracted at the sight of a car driving itself—an unusual sight even in California, where GM and Cruise are permitted to operate autonomously—and fell over during a double-take.

But the case does raise another interesting question. If the case is found in Nilsson's favor, whose responsibility is the crash? Is it the driver of the car, even though it was operating autonomously at the time? Is it Cruise and/or GM's responsibility that the car did not react to Nilsson's presence appropriately?

This will be a case to keep an eye on since it could finally set a precedent to answer the question of who is responsible when an autonomous car crashes.